Controlled switching of a switching device

Abstract

Approaches for controlled switching of a switching device are described. In an example, determining a first rate of decrease of dielectric strength (RDDS) value and a second RDDS value is determined. Once determined, the first RDDS value is compared with an absolute peak value of a gap voltage. If the first RDDS value is less than the absolute peak value of any one of the plurality of half cycles of the gap voltage, switching of the switching device at a second time instant may be performed. To this end, the second time instant is an offset with respect to the first time instant such that the absolute peak value of the gap voltage is not to intersect with the range defined by the first RDDS value and the second RDDS value.

Description

CONTROLLED SWITCHING OF A SWITCHING DEVICEBACKGROUND

[0001] Switching devices, such as a circuit breaker, are electromechanical devices used in the power transmission and distribution system to connect or disconnect various power system components in any electrical circuit. Circuit breakers are capable of making, carrying, and breaking power transmission between different power system components by switching between an open state (i.e. , by de-energizing) and a closed state (i.e., by energizing). Such switching may be controlled using an intelligent electronic device (IED) or relay. The IED either wirelessly or through wired means enables switching of the circuit breaker. With present technical solutions, switching control devices identify switching point on a reference voltage and corresponding switching time instant based on a phase angle.BRIEF DESCRIPTION OF FIGURES

[0002] Systems and / or methods, in accordance with examples of the present subject matter are now described and with reference to the accompanying figures, in which:

[0003] FIG. 1 illustrates a power transmission system with an intelligent electronic device for performing controlled switching of a switching device, as per an example;

[0004] FIG. 2 illustrates a block diagram of an intelligent electronic device, as per an example;

[0005] FIG. 3 illustrates a graph depicting a gap voltage present across the terminals of a switching device, as per an example;

[0006] FIGS. 4-7 illustrates graphs depicting shifting of switching instant from a first time instant to a second time instant, as per an example;

[0007] FIG. 8 illustrates a graph depicting an output voltage present at a load of a power transmission system if switching occurred at a non-optimized switching time instant, as per an example;

[0008] FIG. 9 illustrates a graph depicting an output voltage present at a load of a power transmission system after switching a switching device using present subject matter, as per an example; and

[0009] FIGS. 10A-10B illustrate a method for shifting a switching instant of a switching device from a first time instant to a second time instant, as per an example.DETAILED DESCRIPTION

[0010] An electric power transmission system includes various components, such as resistances, capacitors, inductances, and transformers, which may be connected with each other in different topologies for enabling transmission of power from a source to a destination. Such transmission of power enables distribution of power to areas which are located at a distance from a power supply source. To achieve the desired level of power quality and availability in any power system, switching devices may be placed at appropriate locations along different points in the power transmission system. A switching device, such as circuit breaker, is an electrical switch which has the function of opening and closing to make or break connection between different portions of the power transmission system. In an example, making or breaking connection between different portions of the power transmission system secures the components present in the transmission system against abnormal operational conditions, such as interruptions experienced during fault currents on the power transmission system, switching over voltages, and such. In addition, circuit breakers are also used during normal switching operations as well to ensure a performant operation of the entire transmission system.

[0011] In an example, the circuit breaker may be used as the electric switch between a first portion and a second portion of the power transmission system. In an example, the first portion may be a source-side portion which delivers power, i.e. , the power source and the second portion may be an electrical circuit that consumes the power, i.e., the load. In operation, the circuit breakers may be controlled to switch between an open state (i.e., de-energized state) and a closed state (i.e., energized state) to either break or make connection between the first portion and the second portion of the power transmission system. While such a switching is taking place, certain conditions may arise that may pose a risk to the operational life of other components that may be present along the transmission system. Such risk is caused due to uncontrolled switching of the circuit breakers.

[0012] For example, during an uncontrolled closing operation, i.e., when the circuit breaker switches from open state to closed state in a random manner, certain transient currents may be generated. On the other hand, during an uncontrolled opening operation, i.e., when the circuit breaker switches from closed state to open state due a fault interruption, a transient recovery voltage may appear across the terminals ofthe circuit breaker which may impact the ability of the circuit breaker to interrupt fault currents and maintain power system stability. The instance of occurrences of such transients during operation of the circuit breaker may not be reduced completely, however, the negative effect of such transients on the components of the power transmission system may be prevented through controlled switching effected by the switching device.

[0013] Controlled switching refers to implementing switching of circuit breakers between the open state and the closed state at an appropriate instant of time. The switching of circuit breaker between different states is accomplished in such a manner that the effect of transients would be minimum. In general, controlled switching is a method for eliminating harmful transients by time-controlled switching operation. In an example, control instructions for operating the circuit breakers may be delayed in such a way that making or contact separation occur at an optimum time instant.

[0014] To generate such control instructions, an intelligent electronic device ( I ED), e.g., a modem numerical relay or a controller, may be used. The IED control the closing and opening of independent pole of the circuit breaker with respect to a phase angle of an electrical reference voltage or current, and at certain specific time instants determined based on the phase angle. As described above as well, the circuit breaker may be used to connect the first portion with the second portion of the power transmission system. In such cases, the IED connected to the circuit breaker may issue control instructions to switch the state of the circuit breaker at certain values of the gap voltage which is measurable at the circuit breaker. It may be noted that, while issuing control instruction, the IED may factor in an operating time (i.e., mechanical time required by the switching device to move from one state to another) to appropriately time the operation of the switching device. In addition to the operating time, there are several electrical and mechanical properties of the switching device which may change over time with persisting usage of the circuit breaker, which needs to be considered as well while issuing control instructions.

[0015] As may be understood, the circuit breaker may include certain movable parts which may be controlled mechanically to open or close, in response to switching instructions. Such movable parts may be enclosed in a chamber having a dielectric environment to prevent or quench electrical discharges which may occur during switching. During closing operation, i.e., switching of circuit breaker from open state to closed state, the movable components move closer to each other against areference voltage, i.e., a gap voltage which is present across the terminals of the circuit breaker. With reference to above-described scenario, the gap voltage may be defined as a voltage difference between the first portion, i.e., power source, and the second portion, i.e., load, of the power transmission system. During movement of movable components, the voltage gradient between the movable parts increases and when it becomes greater than the dielectric potential of the dielectric present in the chamber, the arcing occurs.

[0016] It may be noted that with persistent breaking or making operations, certain mechanical and electrical properties of the switching device may change over time resulting in deviations in operating time of the switching device from its ideal operating time. Therefore, the determination of a time instant at which the circuit breaker is to be switched from its current state is also dependent on certain factors, such as mechanical and electrical properties, of the circuit breaker. The IED considers changes in these properties to determine the actual operating time of the switching device ranging between a minimum operating time to a maximum operating time, so that the command is generated and communicated in time for hitting the controlled switching targets.

[0017] Based on a detected anomaly on the transmission line, the IED generates several types of control instructions, e.g., opening instruction, closing instruction, and re-closing instruction. Amongst these instructions, the re-closing instruction require a precise determination of switching instant as it involves switching against the gap voltage which is present between the terminals of the circuit breaker. It may be noted that, before re-closing, the circuit breaker would have tripped or opened, e.g., due to detected fault, which results in a load voltage to be present along the load line of the power transmission system. When transmission lines have series / shunt compensations, i.e., presence of capacitance and inductance in form of shunt reactor, the load voltage after tripping will be a gradually damped sinusoidal oscillated waveform.

[0018] Since the power supply already has certain voltage with corresponding frequency, and the load also have load voltage whose frequency is defined or determined based on the capacitances and inductances placed in the transmission line, there will be a gap voltage present across the terminal of the circuit breaker. As may be understood, the frequency of the load voltage is different (to be precise it is lower) from the frequency of the power supply, resulting in an amplitude modulatedvoltage present across the terminals of the circuit breaker. In view of this, the shape, i.e. , peak value and time period, of such gap voltage is determined based on the extent of compensation present on the transmission line. As a result, the peak value and half cycle time period of consecutive cycles of the gap voltage form an asymmetric sinusoidal voltage during the re-closing operation.

[0019] A controlled switching device may issue control instructions for the switching device to perform switching at a time instant at which the gap voltage is either zero or is at a peak value. The determination of such time instant is performed using the phase angle as a reference for the gap voltage. For example, the IED may continuously determine instants when the reference voltage (e.g., gap voltage measured across the terminal of the circuit breaker) passes through the zero crossings. Upon receipt of a switching command or requirement, the IED calculates the delay time, by keeping in mind various electrical and mechanical aging factor, necessary for switching at the configured target angle with circuit breaker’s operating time considered. To do so, the IED may determine a set of values of the gap voltage over a predefined time period. Based on the determined set of values, the IED is able to learn the pattern related to occurrences of zero crossing in the gap voltage. Since the gap voltage is of periodic nature having definite time period, based on the learned pattern, the IED is able to predict a time instant in future based on the phase angle of the gap voltage for performing controlled switching of the circuit breaker.

[0020] It may be noted that the process of identifying appropriate instant of time by using a phase angle as an identifier is possible only if the gap voltage is periodic, i.e., the shape and time period of the gap voltage remains same. However, as described above, due to presence of various compensation components on the transmission line, the gap voltage measured across the terminals of the circuit breaker is asymmetric in nature. In such a case, prior approaches which use phase angle as a factor to predict appropriate instant of switching on gap voltage may not be useful as the gap voltage is asymmetric. Therefore, there is a need for such a technique which helps in identifying optimum time instant on an asymmetric gap voltage to effectuate controlled switching of the switching device.

[0021] Approaches for controlling a switching device, are described. In an example, the switching device (interchangeably referred to as a circuit breaker), may be controlled at appropriate instants by an intelligent electronic device (IED). Based on identified appropriate time instant, a control instruction would be generated by IEDto be transmitted to the switching device for effecting the switching of the circuit breaker. While identifying appropriate time instant and an operating time of the switching device based on electrical and mechanical aging factors, the IED may record instances when a rate of decrease of dielectric strength (RDDS) value is equal or less than an absolute peak value of a gap voltage. Based on such instances, IED accordingly may control the switching of the switching device such that the switching time instant is shifted by an offset with respect to a first time instant (non-optimized switching time instant) to a second time instant (i.e., an optimized switching time instant). It may be noted that the reference to RDDS (or interchangeably referred to as RDDS value) refers to a line which extends between a point depicting an RDDS for any given instant and a target point at which switching may be performed. The RDDS value (e.g., a first RDDS value) may then be compared to the gap voltage. In the present example, the RDDS value may thus be compared with the absolute peak value of a gap voltage to ascertain whether the RDDS value is less than or equal to the absolute peak value of a gap voltage.

[0022] In operation, initially, a first RDDS value and a second RDDS value. As described above as well, persisting connection breaking or making operations may lead to changes in mechanical and electrical properties of the switching device. Such changes may also affect dielectric strength of the circuit breaker resulting in scattering in RDDS values. As a result of such scattering, the switching device may be such that it have RDDS values that may vary between a minimum RDDS value, represented by first RDDS value and a maximum RDDS value, represented by second RDDS value, with the intervening RDDS values defining a voltage channel between the first RDDS value and the second RDDS value, within which the RDDS value for a given switch may vary.

[0023] In an example, the first time instant, at which the first RDDS value and the second RDDS values are determined, is the instant at which if the switching of the switching device if performed would result in an uncontrolled switching. In an example, the first-time instant is determined based on a switching instant voltage at which the switching needs to be performed with operating time and other aging factors of the switching device considered. For example, power transmission systems having capacitors at load require switching to be effectuated at zero gap voltage. On the other hand, power transmission systems having inductances at load require switching to be effectuated at the peak gap voltage. However, keeping in mind the asymmetric natureof the gap voltage in combination with other aging factors, causing to control switching of the switching device at this time instant, referred to as first time instant, may not be appropriate. Therefore, IED processes the RDDS values with respect to various absolute values of gap voltage measured at the terminals of the circuit breaker.

[0024] Returning to the present example, the first RDDS value is compared with an absolute peak value of the gap voltage which is measured across the terminals of the switching device. To calculate the same, the IED may continuously measure gap voltage which is present across the terminal of the switching device, based on which the absolute values of the gap voltage may be determined. Then, the absolute peak value of the gap voltage is obtained from the absolute values of the gap voltage. In one example, the absolute peak value of a plurality of half cycles of the gap voltage.

[0025] Continuing further, based on the result of the comparison, when it is determined that any the first RDDS value is less than the absolute peak value of the gap voltage, IED controls switching of the switching device at a second time instant which is offset with respect to the first time instant. The offset is determined in such a manner that the absolute peak values of any of the half cycles of the gap voltage is not present within the voltage channel defined between the first RDDS value and the second RDDS value. As described above as well, the first RDDS value and the second RDDS value define the voltage channel between which the RDDS value of a given switching device may vary, ranging from the first RDDS value to the second RDDS value. If in case, the absolute peak value of any of the half cycle preceding the first time instant lies in this voltage channel, then it likely that a connection between the first portion and the second portion of the transmission system may occur intermittently at such absolute values of the gap voltage which is equal to the RDDS values leading to undesirable transients to flow in the transmission system and may cause damage to different components of the transmission system.

[0026] As a result of shifting the first time instant by the offset, the second time instant for switching the switching device is thus determined. It may be noted that, by switching the switching device at second time instant, the non-optimized instants when the absolute value of gap voltage is equal to the RDDS value are neglected successfully to effectuate switching at optimum time instant. In an example, once the IED determines the shifted time instant, i.e., the second time instant, a control instruction or controlled switching command is issued by the IED for the circuit breaker.

[0027] The above explained approaches enable controlled switching of the switching device at such an instant of time such that the effects of transient currents, are reduced. Since the RDDS values are compared with the absolute peak value of gap voltages of more than one preceding half cycles, the instances of pre-arcing are reduced in such a manner that a direct contact making arcing will be performed at the second time instant. It may be noted that, the determination of shifted time instant with respect to plurality of RDDS values helps in neutralizing scattering caused by aging factors of the switching device.

[0028] FIG. 1 illustrates a power transmission system 100 enabling transmission of power from a source to a destination, as per one example. The power transmission system 100 (referred to as system 100) includes a power source 102 which is to provide power to a load 104. In an example, as depicted in FIG. 1 , the power source 102 is communicatively connected with the load 104 via a transmission line 106 to provide power to the load 104. In another example, the load 104 may be the transmission line itself which is acting as a load. It may be noted that, although only transmission line 106 is depicted as a connecting medium for connecting power source 102 with the load 104, however, any other components, such as transformers, may also be deployed in the network without deviating from the scope of the present subject matter.

[0029] The system 100 may further include a switching device 108 which is to act as an electric switch between the power source 102 and the load 104 having the function of making or breaking connection between the power source 102 and the load 104. In an example, the switching device 108 is to allow opening or closing of the circuit as per the situation or requirement of the system 100. For example, if initially the switching device 108 is in a closed state and a high inrush current (i.e. , short circuit current) is detected, the switching device 108 is caused to be switched to an open state to prevent damage which may have been caused due to high inrush current to different components of the system 100. On the other hand, if initially the switching device 108 is in the open state and a voluntary switching instruction is detected for transferring power transmission from one route to another route, the switching device 108 may be caused to switch to the closed state to make a connection between the power source 102 and the load 104. In an example, the switching of the switching device 108 between different states are caused by issuing corresponding control instruction for the switching device 108.

[0030] As described above as well, to reduce damage caused by the transients and other such effects which may occur due to uncontrolled switching of switching device 108, controlled switching of the switching device 108 needs to be performed. In an example, controlled switching refers to causing the switching of the switching device 108 between the open state and the closed state at an appropriate instant of time, i.e., the switching of switching device 108 between different states is accomplished in such a manner that the effect of transients or other such effects, would be minimum. In an example, to accomplish controlled switching, based on the determined controlled switching instant, the control instructions causing making and breaking of the connection in the switching device 108 are delayed in such a way that making or contact separation occur at the optimum time instant.

[0031] To generate such control instructions, the system 100 further includes an intelligent electronic device (IED) 110 which is communicatively connected to the switching device 108. In an example, IED 110 may be a numerical relay or a controller having computing capabilities. The IED 110, in an example, control the closing and opening of the pole of the switching device 108 at certain specific time instants. As described above as well, the switching of the switching device 108 may be performed in various situations, e.g., on detection of fault in the transmission line 106 and during normal switching process. Therefore, based on the requirement, the IED 110 connected to the switching device 108 may generate control instructions to switch the state of the switching device 108. In an example, the IED 110 may further include a switching engine 112 and a clock 114. The switching engine 112 performs determination of switching instant and accordingly generate control instructions for the switching device 108. The clock 114 is a universal clock that may synchronize the switching across various lEDs present across the system 100 (the various possible functions of the clock 114 is described in later paragraphs).

[0032] In furtherance to this, the system 100 may include a pair of voltage transformers (116, 118) for measuring voltage present at different sections of the network. For example, as depicted in FIG. 1 , the voltage transformer 116 is connected to power source 102 side of the system 100 and the voltage transformer 118 is connected to load 104 side of the system 100. In an example, the pair of voltage transformers 116, 118 may further be connected to the IED 110 to provide voltage values to IED 110. In an example, voltage transformer 116 provides voltage present at the power source 102 and the voltage transformer 118 provides voltage valuepresent at the load 104. It may be noted that, although only limited number of components are depicted in system 100 as represented in FIG. 1 , any other components, such as transformers, capacitors, resistors, and inductors, may also be deployed in the system 100 without deviating from the scope of the present subject matter.

[0033] In operation, the switching engine 112 of the IED 110 determines a first RDDS value and a second RDDS value. As described previously, the first RDDS value and the second RDDS value define a voltage channel with an intermediate RDDS value that may be defined between the first RDDS value and the second RDDS value. In an example, persisting connection breaking or making operations may lead to changes in mechanical and electrical properties of the switching device. Such changes may also affect dielectric strength of the circuit breaker resulting in scattering in RDDS values. As a result of such scattering, the switching device may have a minimum RDDS value, represented by first RDDS value and a maximum RDDS value, represented by second RDDS value.

[0034] In an example, the determination of the first RDDS value and the second RDDS value is triggered on receiving a switching command 120 for switching the switching device 108. In an example, IED 110 may transmit or receive one or more the switching command 120 either wirelessly or through wired means for switching the switching device 108. In another example, the switching command 120 is provided by an operator manually to the IED 110. The switching command 120 is received by the IED 110 on occurrence of various scenarios. Examples of such scenarios include, but are not limited to, on detection of fault in the transmission line 106 and for normal switching of the switching device 108. Based on the switching command 120, the switching engine 112 calculates the first time instant and determines a corresponding switching instant voltage of the gap voltage at which the switching of the switching device is instructed to do.

[0035] The first time instant, i.e. , the instant corresponding to which, say, the first RDDS value is determined, is the instant at which if the switching of the switching device may be performed may result in uncontrolled switching. In an example, the first time instant is determined by the IED 110 based on a switching instant voltage at which the switching needs to be performed, considering an operating time and other aging factors of the switching device considered. For example, in case the system 100 have capacitors at load 104, then the switching needs to be effectuated at zero gap voltage.On the other hand, in case the system 100 have inductances at load 104, then the switching needs to be effectuated at the peak gap voltage. However, keeping in mind the asymmetric nature of the gap voltage in combination with other aging factors, such as changes in electrical and mechanical properties, the switching of switching device 108 at first time instant may not be appropriate. Therefore, the switching engine 112 process the RDDS values (e.g., the first RDDS value) with respect to various absolute values of gap voltage which is measured across the terminals of the switching device 108 to determine an optimum switching instant.

[0036] In an example, the switching engine 112 compares the first RDDS value values with an absolute peak value of the gap voltage. In an example, the switching engine 112 of the IED 110 continuously measures gap voltage which is present across the terminal of the switching device 108. Thereafter, the measured gap voltage is processed by performing a modulus operation to convert negative values of gap voltage into positive to obtain the absolute values of the gap voltage. Thereafter, the switching engine 112 obtains the absolute peak value of the gap voltage from the various absolute values of the gap voltage to compare with the plurality of RDDS values. In one example, the absolute peak value corresponds to one of a plurality of half cycles of the gap voltage which are measured at an instant preceding the first time instant.

[0037] Returning to the present example, based on the result of the comparison, when it is determined that any one of the RDDS values, say the first RDDS value, is less than the absolute peak value of any of the plurality of half cycles of the gap voltage, the switching engine 112 controls switching of the switching device at a second time instant which is shifted by an offset with respect to the first time instant. The offset with respect to the first time instant is determined in a manner such that the absolute peak value of any of the plurality of half cycles of the gap voltage is not present within a voltage channel defined by the first RDDS value and the second RDDS value. As described above, the plurality of RDDS values define the voltage channel where the RDDS value may vary between the first RDDS value to the second RDDS value. If in case the absolute peak value of any of the half cycle preceding the first-time instant lies in this voltage channel, it means that the switching device may switch from one state to another multiple times at various instant when the absolute values of the gap voltage is equal to the RDDS values. Such frequent making orbreaking connection in a small interval of time results in transients to flow in the system 100 causing damage to different components of the system 100.

[0038] As a result of shifting the first time instant by the offset to another time instant, i.e., the second time instant for switching the switching device 108 is determined. It may be noted that by switching the switching device 108 at second time instant, the non-optimized instants when the absolute value of gap voltage is equal to the RDDS value is neglected successfully to effectuate switching at the second time instant, i.e., the optimum time instant. In an example, once the shifted time instant, i.e., the second time instant is determined, the switching engine 112 generates and communicates a controlled switching command, such as command 122, to the switching device 108 to cause switching of the switching device 108 at the second time instant.

[0039] The functioning and operation of the IED 110 in various situations is further explained in conjunction with FIG. 2. FIG. 2 depicts various functional blocks of the IED 110, as an example. As per FIG. 2, the IED 110 includes a processor 202, interface(s) 204, and memory(s) 206. The processor 202 may be implemented as microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, and / or other devices that manipulate signals based on operational instructions. The interface(s) 204 may allow the connection or coupling of the IED 110 with one or more devices (such as switching device 108), through a wired (e.g., Local Area Network, i.e., LAN) connection or through a wireless connection (e.g., Bluetooth®, Wi-Fi). The interface(s) 204 may also enable intercommunication between different logical as well as hardware components of the IED 110, such as the clock 114 and switching engine 112 of the IED 110.

[0040] The memory(s) 206 may be a computer-readable medium, examples of which include volatile memory (e.g., RAM), and / or non-volatile memory (e.g., Erasable Programmable read-only memory, i.e., EPROM, flash memory, etc.). The memory(s) 206 may be an external memory, or internal memory, such as a flash drive, a compact disk drive, an external hard disk drive, or the like. The memory(s) 206 may further include data which either may be utilized or generated during the operation of the IED 110.

[0041] The IED 110 may further include engine(s) 208 and data 210. The engine(s) 208 may be implemented as a combination of hardware and programming, for example, programmable instructions to implement a variety of functionalities of theengine(s) 208. In examples described herein, such combinations of hardware and programming may be implemented in several different ways. For example, the programming for the engine(s) 208 may be executable instructions. Such instructions may be stored on a non-transitory machine-readable storage medium which may be coupled either directly with the IED 110 or indirectly (for example, through networked means). In an example, the engine(s) 208 may include a processing resource, for example, either a single processor or a combination of multiple processors, to execute such instructions. In the present examples, the non-transitory machine-readable storage medium may store instructions that, when executed by the processing resource, implement engine(s) 208. In other examples, the engine(s) 208 may be implemented as electronic circuitry.

[0042] The engine(s) 208 includes a transceiver engine 212, the switching engine 112 and other engine(s) 214. The other engine(s) 214 may implement functionalities that supplement functions performed by the IED 110 or any of the engine(s) 208. The data 210, on the other hand, includes data that is either stored or generated as a result of functions implemented by any of the engine(s) 208 or IED 110. It may further be noted that information stored and available in data 210 may be utilized by the engine(s) 208 for performing various functions by the IED 110. In an example, data 210 may include first time instant 216, RDDS value(s) 218, absolute gap voltage value (s) 220, absolute peak value(s) 222, second time instant 224, and other data 226. It may be noted that such examples are only indicative. Other types of data may also be stored or available within the IED 110. Such examples would also fall within the scope of the present subject matter.

[0043] As described previously, the functioning of the IED 110 is to monitor and control functioning of various devices installed in the system 100 by either transmitting signals or receiving signals from such devices. Therefore, to synchronize timing of such signals a highly accurate clock, such as the clock 114, that obtains and maintains time information from an external time source, such as GPS or radio time broadcasts is maintained by the IED 110. The clock 114 also helps in synchronizing actions of different devices present in the system 100. Further, in some cases, the IED 110 may tag events or conditions that may be occurring in the system 100, with a time stamp using clock 114 as reference for sharing with a central server for enabling monitoring of the events that may occur in the system 100. Furthermore, the clock 114 may beutilized by the IED 110 to generate a time synchronized control instruction to the switching device 108.

[0044] In operation, the IED 110 may monitor and control operation of the switching device 108 for generating controlled switching command for the switching device 108. At the outset, the transceiver engine 212 of the IED 110 receives a switching command such as switching command 120, through a transceiver component (not shown in FIG. 2). In an example, the switching command 120 may be received from an external device such as remote terminal unit (RTUs) for performing switching of the switching device 108. The switching command 120 may further include a switching instant voltage as well. In an example, the switching instant voltage indicates the gap voltage value at which the switching of the switching device needs to be performed. Examples of switching instant voltage includes, but are not limited to, a zero voltage and a peak voltage of the gap voltage. For example, as described above as well, when load 104 includes capacitance, the switching of the switching device 108 needs to be performed at zero voltage and when load 104 includes inductances, the switching of the switching device 108 needs to be performed at peak voltage.

[0045] Returning to the present example, the switching command 120 may be generated and received by the IED 110 in various scenarios. For example, on detecting occurrence of conditions, such as fault in the transmission line 106, or voluntary request for switching, the RTU may generate the switching command 120 to be transmitted to the IED 110 for subsequently causing switching of the switching device 108. The controlled switching of the switching device 108 enables controlling and protecting the components implemented on the system 110. In another example, the switching command 120 may be generated by an operator who may be manually monitoring the system 100 for such faults or may be manually controlling switching.

[0046] Once received, the switching engine 112 calculates a first time instant, such as first time instant 216, based on the received switching command 120. In one example, the first time instant 216 is calculated by adding an operating time of the switching device 108 and a delay which is needed to cause switching at the switching instant voltage on the gap voltage. For example, if the switching command 120 is received at time ti and the switching instant voltage is indicated as zero crossing voltage in the switching command 120, the switching engine 112 accordingly calculates the first time instant as ti + t2 + delay time, wherein the t2 is the operating time of the switching device from one state to the another and the delay time is thetime required in addition to ti + t2 to cause switching at the required switching instant voltage.

[0047] Once the first time instant 216 is calculated, the switching engine 112 determines a first RDDS value and a second RDDS value (collectively referred to as RDDS value(s) 218) of the switching device 108 at the first time instant 216. It may be noted that the RDDS value(s) 218 provide a range or channel between which the RDDS value of the switching device 108 may vary. In an example, intermediate RDDS value indicate notional RDDS value, the first RDDS value being the minimum RDDS value and the second RDDS value being the maximum RDDS value of the switching device 108. The first and second RDDS values indicate scattering or variations that may be present in RDDS value of the switching device 108 due to electrical and mechanical aging of the switching device 108. Such aging of the switching device 108 may be caused due to persistent usage of the switching device 108. Therefore, the RDDS value(s) 218 may define the voltage channel between the first RDDS value to the second RDDS value (the same is described in conjunction with FIGS. 4-8).

[0048] It is again emphasized that a reference to RDDS (or interchangeably referred to as RDDS value) refers to a line which extends between a point depicting an RDDS for any given instant and a target point at which switching may be performed for a switching device, such as the switching device 108. The RDDS value (e.g., a first RDDS value) may then be compared to the gap voltage. In the present example, the RDDS value may thus be compared with the absolute peak value of a gap voltage to ascertain whether the RDDS value is less than or equal to the absolute peak value of a gap voltage.

[0049] In an example, if the first time instant 216 determined by the switching engine 112 requires a high RDDS for the switching device 108, i.e., the peak value of the half cycle just before the first time instant 216 is higher than a threshold value, then the switching engine 112 shifts the first time instant 216 to a subsequent half cycle of the gap voltage or skips the next half cycle of the gap voltage. In an example, once RDDS value(s) 218 are determined, the switching engine 112 compares the RDDS value(s) with a threshold value. Based on the result of comparison, on determining that any one of the RDDS value(s) 218 to exceed the threshold value, the switching engine 112 shifts the first time instant 216 to a subsequent half cycle of the gap voltage. In an example, the threshold value is the maximum limit of RDDS beyond which the switching device 108 is unable to operate.

[0050] Returning to the present example, the switching engine 112 compares the RDDS value(s) 218 with an absolute peak value, such as absolute peak value 222 of the gap voltage which is present across the terminals of the switching device 108. In an example, a set of values of the gap voltage is determined by the switching engine 112 based on the voltage readings received from the pair of voltage transformers 116, 118 (as depicted in FIG. 1 ). For example, the switching engine 112 obtain supply side voltage (Vs) from the voltage transformer 116 and load side voltage (VL) from the voltage transformer 118 which is present at the load side of the system 100. Based on the obtained Vs and VL, the switching engine 112 determines gap voltage present across the terminals of the switching device 108. In another example, the switching engine 112 obtains the gap voltage values from the switching device 108 itself. Once obtained, the switching engine 112 convert the gap voltage values to absolute values of the gap voltage, such as absolute gap voltage value(s) 220 for converting negative values of the gap voltage to positive resulting in formation of plurality of positive half cycles. Once the absolute gap voltage value(s) are determined, the switching engine 112 obtain the absolute peak value(s) 222 of the gap voltage from the absolute gap voltage value(s) 220 of the gap voltage. In one example, the absolute peak value(s) 222 corresponds to peak value of one of a plurality of half cycles present within the gap voltage which are measured at an instant preceding the first time instant 216.

[0051] Returning to the present example, based on the comparison, when it is determined that the first RDDS value of RDDS value(s) 218 is less than the absolute peak value(s) 222 of any one of the plurality of half cycles of the gap voltage which are measured at an instant preceding the first time instant 216, the switching engine 112 causes to control switching of the switching device at a second time instant 224 which is offset with respect to the first time instant 216.

[0052] In one exemplary implementation, when it is determined that the first RDDS value, i.e., the minimum RDDS value, is less than the absolute peak value of the half cycle of the gap voltage and the switching instant voltage is zero, the switching engine 112 cause to control switching of the switching device 108 at the second time instant 224. In the present case, the absolute peak value corresponds to the half cycle which is adjacent to the first time instant, and it is measured at the instant preceding the first time instant 216. Further, the switching instant voltage is derived from the switching command 120 received from the external device. In an example, the second time instant 224 is determined by delaying the first time instant 216 by an offset and theoffset is determined in such a manner that the absolute peak value of the considered half cycle is not within the voltage channel defined by the RDDS value(s) 218.

[0053] In another exemplary implementation, when it is determined that the first RDDS value is greater than the absolute peak value of the half cycle, which is adjacent and preceding the first time instant 216 of the gap voltage and the switching instant voltage is zero, the switching engine 112 determines a first peak value of a first half cycle and a second peak value of a second half cycle. In an example, the first half cycle is adjacent and preceding the first time instant 216 and the second half cycle is adjacent and occurring after the first time instant 216. Once determined, the switching engine 112 compares the first peak value with the second peak value.

[0054] Based on the comparison, when it is determined that the first peak value is less than the second peak value, the switching engine 112 identifies a plurality of instants when the RDDS value(s) 218 is equal to the absolute values of the half cycles of the gap voltage. In an example, the absolute values of those half cycles are considered which are measured at the instant preceding the first time instant 216. In an example, the plurality of instants includes an earliest pre-strike instant and a later pre-strike instant. Once identified, the switching engine 112 causes the switching of the switching device 108 at the second time instant 224 which is delayed by the offset with respect to the first time instant 216. Further, the amount of offset is determined by the switching engine 112 in such a manner that the earliest pre-strike instant becomes the later pre-strike instant, i.e. , the latest pre-strike instant becomes the only time instant at which the RDDS value(s) 218 equals the absolute values of the gap voltage.

[0055] In another example, when it is determined that the first peak value is greater than the second peak value, the switching engine 112 identifies the plurality of instants when one of the RDDS value(s) 218 is equal to the absolute values of the half cycles of the gap voltage. Once identified, the switching engine 112 causes the switching of the switching device 108 at the second time instant 224 which is delayed by the offset with respect to the first time instant 216. In an example, the amount of offset is determined by the switching engine 112 in such a manner that the earliest pre-strike instant becomes the pre-strike instant, i.e., the instant becomes the only time instant at which the RDDS value(s) 218 equals the absolute values of the gap voltage.

[0056] In yet another exemplary implementation, when it is determined that the second RDDS value, i.e., the maximum RDDS value, is less than the absolute peakvalue of the half cycle of the gap voltage and the switching instant voltage is peak voltage, the switching engine 112 cause to control switching of the switching device 108 at the second time instant 224. In the present case, the absolute peak value corresponds to the half cycle which is adjacent to the first time instant, and it is measured at instant preceding the first time instant 216. Further, the switching instant voltage is derived from the switching command 120 received from the external device. In an example, the second time instant 224 is determined by pre-empting the first time instant 216 by an offset and the offset is determined in such a manner that the absolute values of the half cycle which is measured at instant proceeding the first-time instant is not present within the voltage channel defined by the RDDS value(s) 218.

[0057] In yet another exemplary implementation, when it is determined that the second RDDS value is greater than the absolute peak value of the half cycle, which is adjacent and preceding the first time instant 216, of the gap voltage and the switching instant voltage is peak voltage, the switching engine 112 identifies a plurality of instants when one of the RDDS value(s) 218 is equal to the absolute values of the half cycles of the gap voltage. In an example, the absolute values of those half cycles are considered which are measured at the instant preceding and proceeding the first time instant 216. In an example, the plurality of instants includes an earliest pre-strike instant and a latest pre-strike instant. Once identified, the switching engine 112 causes the switching of the switching device 108 at the second time instant 224 which is preempted by the offset with respect to the first time instant 216. In an example, the amount of offset is determined by the switching engine 112 in such a manner that the earliest pre-strike instant and the latest pre-strike instant have similar absolute value of gap voltage.

[0058] As a result of such offsetting, the switching engine 112 generates a controlled open / close command 122 to be transmitted to the switching device 108 for initiating switching of the switching device 108 at the second time instant 224. In an example, the switching device 108 may be switched from one state to another. Examples of such states includes an energized state (i.e. , the closed state) and a deenergized state (i.e., the open state). The manner in which the shifting of the first time instant by the offset to the second time instant is achieved in view of different conditions is described in conjunction with FIGS. 3-7.

[0059] FIG. 3 illustrates a graph 300 which indicates the variation of gap voltage that may be measured across the terminals of a switching device, such as switchingdevice 108. The horizontal axis 302 of the graph 300 represents the time-axis and the vertical axis 304 represents voltage-axis. Graph 300 depicts the variation in the gap voltage (i.e., the gap voltage measurable across the terminals of the switching device 108) denoted as gap voltage 306. As depicted in the graph 300, the gap voltage 306 is asymmetric in nature due to presence of different compensation components at the load 104 side of the system 100. As described above as well, before re-closing, the switching device 108 would have tripped or opened, e.g., due to fault, which is detected over transmission line 106, which results in the load voltage to be present along the load line of the system 100. When transmission lines have series / shunt compensations, i.e., presence of capacitance and inductance in form of shunt reactor, the load voltage after tripping will be a gradually damped sinusoidal oscillated waveform.

[0060] Since the power source 102 already has certain voltage having certain frequency, and the load 104 also have load voltage whose frequency is defined or determined based on the capacitances and inductances placed in the transmission line, there will be a gap voltage, such as gap voltage 306 as depicted in FIG. 3, which is measurable across the terminals of the switching device 108. In general, the frequency of the load voltage is different (to be precise it is lower) from the frequency of the supply voltage, resulting in an amplitude modulated voltage across the terminals of the switching device 108. In view of this, the shape, i.e., peak value and time period, of such gap voltage is not uniform resulting in an asymmetric sinusoidal voltage, such as gap voltage 306, during the re-closing operation.

[0061] The determination of an optimum time instant, such as second time instant 224, on the gap voltage 306 by shifting the first time instant 216 by an offset to either delay or pre-empt the switching of the switching device may be performed by plotting values of RDDS and set of values of gap voltage on a graph. For example, as depicted and explained in conjunction with FIGS. 4-7, the switching engine 112 may generate graphs by plotting RDDS value(s) 218 with the absolute gap voltage value(s) 220. Based on the plotted graph, the switching engine 112 accordingly determine inappropriate pre-strike instant between RDDS value(s) 218 and gap voltage to shift the switching instant by an offset. It may be noted that, the determination of the optimized switching instant by processing RDDS values with the absolute values of the gap voltage using graph theory is exemplary, and the same may be performed using other processing method(s).

[0062] FIGS. 4A-4B depicts the variation of gap voltage (i.e., the voltage measurable across the terminals of the switching device 108) as depicted in FIG. 3 and the plurality of RDDS values. FIG. 4A illustrates a graph 402 and FIG. 4B illustrates a graph 404 indicating the variation in gap voltage and plurality of RDDS values of the switching device 108 with respect to time. The horizontal axis 406 of the graphs (402, 404) represents the time-axis and the vertical axis 408 represents voltage-axis. As depicted in FIG. 4, the variation in voltage measured across the terminals of the switching device in open state is denoted by gap voltage 410 and the plurality of RDDS values of the switching device 108 is denoted by a plurality of RDDS characteristic lines 412. In an example, the plurality of RDDS characteristic lines 412 (referred to as RDDS characteristic lines 412) includes a minimum RDDS characteristic line 414 depicting first RDDS value and a maximum RDDS characteristic line 416 depicting second RDDS value. As described previously, the RDDS value for any given switching device (such as the switching device 108) would vary or experience scatter between the first RDDS value and the second RDDS value, depicted by the minimum RDDS characteristic line 414 and the maximum RDDS characteristic line 416, respectively. These RDDS characteristic lines 412 further include an intermediate RDDS characteristic line 418 depicting a notional RDDS value. In an example, the notional RDDS value (depicted by the intermediate RDDS characteristic line 418) is a value of RDDS for a switching device without the influence of electrical and mechanical aging factors.

[0063] Returning to the present example, on receiving a switching command, such as switching command 120, the switching engine 112 of the IED 110 determines a first time instant, i.e., instant at which if the switching of the switching device may be performed may result in uncontrolled switching. In an example, the switching command 120 may include ani indication of the voltage value at which the switching needs to be performed. Subsequently, the switching engine 112 determines plurality of RDDS values as denoted by RDDS characteristic lines 412 at the first time instant. It may be noted that FIG. 4-6 depicts examples when the switching instant voltage is determined to be zero voltage based on the received switching command 120. As depicted in FIG. 4A, the RDDS characteristic lines 412, specifically minimum RDDS characteristic line 414, intersects with the gap voltage 410 at multiple locations. The intersection of minimum RDDS characteristic line 414 with gap voltage 410 may be regarded as first RDDS value is equal to the absolute values of the half cycle of thegap voltage which is just before the first time instant Ti , i.e. , adjacent and preceding half cycle.

[0064] Since one of the RDDS characteristic lines 412, specifically, minimum RDDS characteristic line 414 is intersecting with gap voltage 410 at other locations as well, the current switching instant, i.e., the first time instant Ti is not optimized one. In an example, when movable parts of the switching device 108 comes closer to transition to closed state, the RDDS value of the switching device 108 decreases with decreased distance between the movable parts. Therefore, at intersection, e.g., at location 422, the RDDS value becomes equal to the gap voltage 410 value causing the switching device 108 to temporarily switch from open state to the closed state, i.e., allowing passage of current, resulting in flow of high inrush current through various components of the system 100. Such high inrush current thereby causes damage to the components of the system 100. Subsequently, as the movable parts move closer further, the RDDS value again becomes greater than gap voltage thereby breaking the temporary connection formed between movable parts. This process continues until the dielectric strength reduces to such an extent that a physical connection is formed between the movable parts. Such recursive making and breaking of connection and corresponding flow of inrush currents negatively affects the performance of various components of the system 100.

[0065] To overcome this problem, the switching engine 112 of the IED 110 causes the first time instant Ti to shift by an offset such that none of the RDDS characteristic lines 412 intersects with the adjacent and preceding half cycle of the gap voltage 410, i.e., the only intersection left between the RDDS characteristic lines 412 and gap voltage 410 is the optimized time instant. For example, as depicted in FIG. 4B, the switching instant may be shifted by the offset, such as offset 426, to right with respect to the first time instant Ti to reach a second time instant T2 corresponding to a switching location 424. As depicted in FIG. 4B, once shifted by the offset, the RDDS characteristic lines 412 does not intersect with the gap voltage 410, except at the second time instant T2, resulting in optimum and transient free switching of the switching device 108, i.e., the movable parts of the switching device 108 makes electrical connection at time instant T2.

[0066] Instances wherein which the RDDS characteristic lines depicting various RDDS values intersects even with multiple half cycles prior to the preceding half cycle of gap voltage are now discussed in relation to the graph depicted in FIGS. 5-6. FIG.5A-B depicts the variation of gap voltage and the RDDS values as described in conjunction with FIG. 1 -2. For example, FIG. 5A illustrates a graph 502 and FIG. 5B illustrates a graph 504 indicating the variation in gap voltage and the RDDS values of the switching device 108 with respect to time. Similar to FIG. 4, the horizontal axis 406 of the graphs (502, 504) represents time and the vertical axis 408 represents voltage. Further, similar to FIG. 4, the gap voltage is denoted by gap voltage 410 and the plurality of RDDS values by plurality of RDDS characteristic lines 412.

[0067] As depicted in conjunction with FIG. 4 as well, on receiving a switching command, such as switching command 120, the switching engine 112 of the IED 110 determines a first time instant Ti , i.e., is the instant at which if the switching of the switching device may be performed may result in uncontrolled switching. Subsequently, the switching engine 112 determines the RDDS values as denoted by RDDS characteristic lines 412 at the first time instant Ti. As depicted in FIG. 5A, the RDDS characteristic lines 412, specifically minimum RDDS characteristic line 414, intersects with the gap voltage 410 at multiple locations. It may be noted that in the present case, the minimum RDDS characteristic line 414 does not intersect with half cycle which is just before the first-time instant T, however, it does intersect with other half cycles which are measured before the first time instant Ti. In such a case, two scenarios arise based on the difference between the peak value of half cycles adjacent to both sides of the first time instant Ti , i.e., a prior half cycle 508 of gap voltage 410 which is adjacent and preceding the first time instant Ti , and with respect to the peak value of a later half cycle, i.e., later half cycle 510 which is adjacent and occurring after the first time instant Ti.

[0068] The first scenario is, when the peak value of the prior half cycle 508 of gap voltage 410 is less than the peak value of the half cycle 510. To determine the same, the switching engine 112 may compare a preceding peak value with a proceeding peak value to determine which is higher. Based on the comparison, on determining the peak value of the prior half cycle 508 of gap voltage 410 is less than the peak value of the half cycle 510, e.g. , the switching engine 1 12 identify a plurality of instants when one of the RDDS characteristic lines 412 intersects with half cycles which are preceding the first time instant Ti. As depicted in FIG. 5, the switching engine 112 identify the plurality of instants when the minimum RDDS characteristic line 414 intersects with the half cycles of the gap voltage which are preceding the first time instant 506, i.e., the first RDDS value is equal to the absolute value of the half cyclesof gap voltage. In an example, the plurality of instant includes an earliest or prior prestrike instant 512 and a later pre-strike instant, i.e. , the first time instant 506.

[0069] Since one of the RDDS characteristic lines 412, specifically, minimum RDDS characteristic line 414 is intersecting with gap voltage 410 at other locations as well, the current switching instant, i.e., the first time instant T1 is not optimized one. To overcome this problem, the switching engine 112 of the IED 110 causes the first time instant Ti to shift by an offset such that the minimum RDDS characteristic lines 414 is to no longer intersect with the preceding half cycles of the gap voltage 410. For example, as depicted in FIG. 5B, the switching instant has been shifted by the offset to right, i.e., the switching instant is delayed, with respect to the first time instant Ti to reach a second time instant T2 corresponding to a switching location 514. As depicted in FIG. 5B, once shifted by the offset, the RDDS characteristic lines 412 no longer is to intersect with the gap voltage 410 resulting in optimum and transient free switching of the switching device 108, i.e., the movable parts of the switching device 108 makes electrical connection at time instant T2.

[0070] The second scenario involves the peak value of the half cycle which is preceding the first time instant is greater than the peak value of the half cycle which is occurring after the first time instant, and is depicted in FIGS. 6A-B. FIG. 6A illustrates a graph 602 and FIG. 6B illustrates a graph 604 indicating the variation in gap voltage and plurality of RDDS values of the switching device 108 with respect to time. As depicted in FIG. 6A-B, the half cycle, denoted as prior half cycle 608, which is adjacent and preceding the first time instant Ti has higher voltage gradient than the half cycle, denoted as later half cycle 610, which is adjacent and occurring after the first time instant Ti . In such a case, the switching engine 112 identifies plurality of instants when the RDDS characteristic lines 412 intersects with the gap voltage 410. For example, as depicted in FIG. 6, the switching engine 112 identify the plurality of instants when the minimum RDDS characteristic line 414 intersects with the half cycles of the gap voltage which are preceding the first time instant Ti , i.e., the first RDDS value is equal to the absolute value of the half cycles of gap voltage 410, i.e., at an earlier pre-strike instant 612 and a later pre-strike instant 606.

[0071] Since one of the RDDS characteristic lines 412, specifically, minimum RDDS characteristic line 414 is intersecting with gap voltage 410 at multiple locations, the current switching instant, i.e., the first time instant Ti is not optimized one. To overcome this problem, the switching engine 112 of the IED 110 causes the first timeinstant Ti to shift by an offset such that the minimum RDDS characteristic lines 414 is to no longer intersect with the preceding half cycles of the gap voltage 410. For example, as depicted in FIG. 6B, the switching instant has been shifted by the offset to right, i.e., the switching instant is delayed, with respect to the first time instant Ti to a second time instant T2 corresponding to a switching location 614. As depicted in FIG. 6B, once shifted by the offset, the RDDS characteristic lines 412 is to no longer intersect with the gap voltage 410 resulting in optimum and transient free switching of the switching device 108, i.e., the movable parts of the switching device 108 makes electrical connection at time instant T2.

[0072] Instances where the switching instant voltage indicated in the switching command 120 is peak voltage value and the corresponding offsetting of the time instant is depicted in FIG. 7. Similar to FIG. 4-6, FIG. 7A-B depicts the variation of gap voltage and the plurality of RDDS values as described in conjunction with FIG. 1 -2. For example, FIG. 7A illustrates a graph 702 and FIG. 7B illustrates a graph 704 indicating the variation in gap voltage and plurality of RDDS values of the switching device 108 with respect to time. Similar to FIG. 4-6, the horizontal axis 406 of the graphs (702, 704) represents time-axis and the vertical axis 408 represents voltageaxis. Further, similar to FIG. 4, the gap voltage is denoted by gap voltage 410 and the plurality of RDDS values by plurality of RDDS characteristic lines 412.

[0073] As described above, on receiving a switching command, such as switching command 120, the switching engine 112 of the IED 110 determines a first time instant, i.e., is the instant at which if the switching of the switching device may be performed may result in uncontrolled switching. In an example, the switching command 120 further includes a switching instant voltage as well indicating the voltage value at which the switching needs to be performed. In the present example, the switching instant voltage is considered to be peak voltage value of the gap voltage. Subsequently, the switching engine 112 determines plurality of RDDS values as denoted by RDDS characteristic lines 412 at the first time instant. As depicted in FIG. 7A, the RDDS characteristic lines 412, specifically maximum RDDS characteristic line 416, intersects with the gap voltage 410 at multiple locations. One of those locations is the first switching location denoted by 706, which is the non-optimized location of switching, and the corresponding time is the first time instant Ti. The intersection of maximum RDDS characteristic line 416 with gap voltage 410 may be regarded as second RDDSvalue is equal to the absolute values of the half cycle of the gap voltage which is just before the first time instant Ti , i.e. , adjacent and preceding half cycle.

[0074] Since one of the RDDS characteristic lines 412, specifically, maximum RDDS characteristic line 416 is intersecting with gap voltage 410 at other locations as well, the current switching instant, i.e., the first time instant Ti is not optimized one. Specifically, the last intersection being on the half cycle of the gap voltage which is adjacent and occurring after the first time instant Ti. In an example, when movable parts of the switching device 108 comes closer to transition to closed state, the RDDS value of the switching device 108 decreases with decreased distance between the movable parts. Therefore, at intersection, e.g., at location 706, the RDDS value becomes equal to the gap voltage 410 value causing the switching device 108 to temporarily switch from open state to the closed state, i.e., allowing passage of current. Subsequently, as the movable parts move closer further, the RDDS value again becomes greater than gap voltage thereby breaking the temporary connection formed between movable parts. This process continues until the dielectric strength reduces to such an extent that a physical connection is formed between the movable parts. The final connection between the movable parts forms at a location 708. However, since the location 708 is not at the peak value of the gap voltage 410, the location 706 is not an optimized switching location.

[0075] To overcome this problem, the switching engine 112 of the IED 110 causes the first time instant Ti to shift by an offset such that none of the RDDS characteristic lines 412 intersects with the adjacent and proceeding half cycle of the gap voltage 410, i.e., the intersection of the RDDS characteristic lines 412 and gap voltage 410 is at the optimized time instant. For example, as depicted in FIG. 4B, the switching instant may be shifted by the offset, to left with respect to the first time instant Ti to reach a second time instant T2 corresponding to a switching location 710. As depicted in FIG. 4B, once shifted by the offset, the RDDS characteristic lines 412 does not intersect with the half cycle which is proceeding the first time instant Ti , resulting in optimum switching of the switching device 108, i.e., the movable parts of the switching device 108 makes electrical connection at time instant T2.

[0076] FIG. 8 illustrates a graph 800 which indicates a load voltage measurable at load 104 on the system 100. The horizontal axis 802 of the graph 800 indicates timeaxis and the vertical axis 804 of the graph 800 indicates voltage-axis. The load voltage, which is denoted by 806, as depicted in FIG. 8 is obtained by reclosing the switchingdevice 108 using at non-optimized switching time instant. As depicted in FIG. 8, the load voltage 806 is continuously changing with irregularly occurring spikes and minimum values, when the switching device 108 is reclosed. Such uncontrolled or nonoptimized switching of the switching device 108 may often cause high transient inrush currents and results in high switching over voltages. These may lead to an increase in circuit breaker wear and may even damage other components of the system 100.

[0077] In contrast to this, the load voltage curve measurable at load 104, when the switching is performed based on the control instructions generated by the switching engine 112 of the IED 110, is more symmetric and having less transients as compared to load voltage 906 as depicted in FIG. 8 thereby causing less damage to the various components of the system 100. For example, as depicted in FIG. 9 by the graph 900, the load voltage, denoted by 902, has smooth peaks and symmetricity which thereby causes less damage to the components installed on the system 100.

[0078] FIG. 10A-10B illustrates a method 1000 for performing controlled switching of a switching device, as per an example. The order in which the above-mentioned method is described is not intended to be construed as a limitation, and some of the described method blocks may be combined in a different order to implement the method, or an alternative method.

[0079] Furthermore, the above-mentioned method may be implemented in a suitable hardware, computer-readable instructions, or combination thereof. The steps of such method may be performed by either a system under the instruction of machine executable instructions stored on a non-transitory computer readable medium or by dedicated hardware circuits, microcontrollers, or logic circuits. For example, the method may be performed by an Intelligent Electronic Device, such as IED 110. In an implementation, the method may be performed under an “as a service” delivery model, where the IED 110, operated by a provider, receives programmable code. Herein, some examples are also intended to cover non-transitory computer readable medium, for example, digital data storage media, which are computer readable and encode computer-executable instructions, where said instructions perform some or all the steps of the above-mentioned methods.

[0080] In an example, the method 1000 may be implemented by the IED 110 for identifying an optimized switching time instant for performing controlled switching of a switching device, such as switching device 108. To this end, at block 1002, a switching command for switching a switching device is received from external devices. Forexample, the transceiver engine 212 of the IED 110 receives a switching command, such as switching command 120, from an external device such as remote terminal unit (RTUs) for performing switching of the switching device 108. In an example, the switching command 120 may be generated based on a switching instant voltage prescribed in the IED 110. In an example, the switching instant voltage indicates the gap voltage value at which the switching of the switching device needs to be performed. The switching voltage may correspond to any value between a zero voltage and a peak voltage value of the gap voltage. For example, as described above as well, when load 104 includes capacitance, the switching of the switching device 108 needs to be performed at zero voltage and when load 104 includes inductances, the switching of the switching device 108 needs to be performed at peak voltage.

[0081] At block 1004, based on the received switching command, a first time instant and a switching instant voltage are determined on a gap voltage. For example, the switching engine 112 calculates a first time instant, such as first time instant 216, based on the received switching command 120. In one example, the first time instant 216 is calculated by adding an operating time of the switching device 108 and a delay which is needed to cause switching at the switching instant voltage on the gap voltage. For example, if the switching command 120 is received at time ti and the switching instant voltage is indicated as zero crossing voltage in the switching command 120, the switching engine 112 accordingly calculates the first time instant as ti + t2 + delay time, wherein the t2 is the operating time of the switching device from one state to the another and the delay time is the time required in addition to ti + t2 to cause switching at the required switching instant voltage.

[0082] At block 1006, of the RDDS values of the switching device are determined at the first time instant. For example, the switching engine 112 determines a first RDDS value and the second RDDS value as provided in the RDDS value(s) 218 of the switching device 108 at the first time instant 216. In an example, the first RDDS value being the minimum RDDS value and the second RDDS value being the maximum RDDS value of the switching device 108. The first and second RDDS values indicate scattering or variations in RDDS value of the switching device 108 due to electrical and mechanical aging of the switching device 108.

[0083] At block 1008, the first RDDS value is compared with a threshold value. For example, if the first time instant 216 determined by the switching engine 112 requires a high RDDS for the switching device 108, i.e. , the peak value of the half cycle justbefore the first time instant 216 is higher than a threshold value, then the switching engine 112 shifts the first time instant 216 to a subsequent half cycle of the gap voltage or skips the next half cycle of the gap voltage. In an example, once RDDS value(s) 218 are determined, the switching engine 112 compares the RDDS value(s) with a threshold value. In an example, the threshold value is the maximum limit of RDDS beyond which the switching device 108 is unable to operate.

[0084] At block 1010, a determination is made whether the compared RDDS value is greater than threshold value. For example, based on the comparison, if is determined that the compared RDDS value is greater than the threshold value (i.e., the ‘Yes’ path from block 1010), then the method proceeds to block 1012 wherein which the first time instant is shifted or offset to a subsequent half cycle of the gap voltage. On the other hand, if it is determined that the compared RDDS value is less than the threshold value (‘No’ path from block 1010), then the method 1000 proceeds to block 1014 (depicted in FIG. 10B).

[0085] At block 1012, the first time instant is shifted to a subsequent half cycle of the gap voltage. For example, the switching engine 112 shifts the present half cycle on which the first time instant 216 is present to the subsequent half cycle as determined RDDS value(s) 218 are going beyond the maximum allowed RDDS value. Thereafter, the method 1000 proceeds to block 1006 for determining RDDS value(s) for the new first time instant.

[0086] At block 1014, the first RDDS value are compared with an absolute peak value of a half cycle of the gap voltage which is measured at an instant preceding the first time instant. For example, the switching engine 112 compares of the first RDDS value specified in the RDDS value(s) 218 with an absolute peak value, such as absolute peak value(s) 222 of the gap voltage which is present across the terminals of the switching device 108. In an example, a set of values of the gap voltage is determined by the switching engine 112 based on the voltage readings received from the pair of voltage transformers 116, 118 (as depicted in FIG. 1 ). For example, the switching engine 112 obtain supply side voltage (Vs) from the voltage transformer 116 and load side voltage (VL) from the voltage transformer 118 which is present at the load side of the system 100. Based on the obtained Vs and VL, the switching engine 112 determines gap voltage present across the terminals of the switching device 108. In another example, the switching engine 112 obtains the gap voltage values from the switching device 108 itself.

[0087] Once obtained, the switching engine 112 convert the gap voltage values to absolute values of the gap voltage, such as absolute gap voltage value(s) 220 for converting negative values of the gap voltage to positive resulting in formation of plurality of positive half cycles. Once the absolute gap voltage value(s) are determined, the switching engine 112 obtain the absolute peak value(s) 222 of the gap voltage from the absolute gap voltage value(s) 220 of the gap voltage. In one example, the absolute peak value(s) 222 corresponds to peak value of one of a plurality of half cycles present within the gap voltage which are measured at an instant preceding the first time instant 216.

[0088] At block 1016, on determining any one of the RDDS values to be less than the absolute peak value of any one of the plurality of half cycles of the gap voltage, a second time instant which is offset with respect to the first time instant is determined. For example, based on the comparison, when it is determined that any one of the RDDS value(s) 218 is less than the absolute peak value(s) 222 of any one of the plurality of half cycles of the gap voltage which are measured at an instant preceding the first time instant 216, the switching engine 112 causes to control switching of the switching device at the second time instant 224 which is offset with respect to the first time instant 216.

[0089] In one exemplary implementation, when it is determined that the first RDDS value, i.e., the minimum RDDS value, is less than the absolute peak value of the half cycle of the gap voltage and the switching instant voltage is zero, the switching engine 112 cause to control switching of the switching device 108 at the second time instant 224. In the present case, the absolute peak value corresponds to the half cycle which is adjacent to the first time instant, and it is measured at the instant preceding the first time instant 216. Further, the switching instant voltage is derived from the switching command 120 received from the external device. In an example, the second time instant 224 is determined by delaying the first time instant 216 by an offset and the offset is determined in such a manner that the absolute peak value of the considered half cycle is not to intersect with the voltage channel defined by the RDDS value(s) 218.

[0090] In another exemplary implementation, when it is determined that the first RDDS value is greater than the absolute peak value of the half cycle, which is adjacent and preceding the first time instant 216 of the gap voltage and the switching instant voltage is zero, the switching engine 112 determines a first peak value of a first halfcycle and a second peak value of a second half cycle. In an example, the first half cycle is adjacent and preceding the first time instant 216 and the second half cycle is adjacent and proceeding the first time instant 216. Once determined, the switching engine 112 compares the first peak value with the second peak value.

[0091] Based on the comparison, when it is determined that the first peak value is less than the second peak value, the switching engine 112 identifies a plurality of instants when the RDDS value(s) 218 is equal to the absolute values of the half cycles of the gap voltage. In an example, the absolute values of those half cycles are considered which are measured at the instant preceding the first time instant 216. In an example, the plurality of instants includes an earlier pre-strike instant and a later pre-strike instant. Once identified, the switching engine 112 causes the switching of the switching device 108 at the second time instant 224 which is delayed by the offset with respect to the first time instant 216. Further, the amount of offset is determined by the switching engine 112 in such a manner that the RDDS value(s) 218 is to no longer intersect the absolute values of the gap voltage.

[0092] In another example, when it is determined that the first peak value is greater than the second peak value, the switching engine 112 identifies the plurality of instants when one of the RDDS value(s) 218 is equal to the absolute values of the half cycles of the gap voltage. Once identified, the switching engine 112 causes the switching of the switching device 108 at the second time instant 224 which is delayed by the offset with respect to the first time instant 216. In an example, the amount of offset is determined by the switching engine 112 in a manner such that the RDDS characteristic line corresponding to RDDS value(s) 218 is to no longer intersect the half cycles of the gap voltage 410.

[0093] In yet another exemplary implementation, when it is determined that the second RDDS value, i.e. , the maximum RDDS value, is less than the absolute peak value of the half cycle of the gap voltage and the switching instant voltage is peak voltage, the switching engine 112 cause to control switching of the switching device 108 at the second time instant 224. In the present case, the absolute peak value corresponds to the half cycle which is adjacent to the first time instant, and it is measured at an instant preceding the first time instant 216. Further, the switching instant voltage is derived from the switching command 120 received from the external device. In an example, the second time instant 224 is determined by pre-empting the first time instant 216 by an offset and the offset is determined in such a manner thatthe absolute values of the half cycle which is measured at instant proceeding the firsttime instant is not present within the voltage channel defined by the RDDS value(s) 218.

[0094] In yet another exemplary implementation, when it is determined that the second RDDS value is greater than the absolute peak value of the half cycle, which is adjacent and preceding the first time instant 216, of the gap voltage and the switching instant voltage is peak voltage, the switching engine 112 identifies a plurality of instants when one of the RDDS value(s) 218 is equal to the absolute values of the half cycles of the gap voltage. In an example, the absolute values of those half cycles are considered which are measured at the instant preceding and proceeding the first time instant 216. In an example, the plurality of instants includes an earliest pre-strike instant and a latest pre-strike instant. Once identified, the switching engine 112 causes the switching of the switching device 108 at the second time instant 224 which is preempted by the offset with respect to the first time instant 216. In an example, the amount of offset is determined by the switching engine 112 in such a manner that the earlier pre-strike instant and the later pre-strike instant have similar absolute value of gap voltage.

[0095] At block 1018, based on the determined second time instant, a controlled switching command to be transmitted to switching device is generated to effectuate switching of the switching device at the second time instant. For example, the switching engine 112 generates a controlled open / close command 122 to be transmitted to the switching device 108 for initiating switching of the switching device 108 at the second time instant 224. In an example, the switching device 108 may be switched from one state to another. Examples of such states includes an energized state (i.e., the closed state) and a de-energized state (i.e., the open state).

[0096] Although examples for the present disclosure have been described in language specific to structural features and / or methods, it is to be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed and explained as examples of the present disclosure.

Claims

I / We Claim:1 . A method for controlled switching of a switching device, the method comprising: determining a first rate of decrease of dielectric strength (RDDS) value and a second RDDS value of the switching device at a first time instant, wherein the first RDDS value and the second RDDS value define a range between which a RDDS value of the switching device is to vary; comparing at least the first RDDS value with an absolute peak value of a gap voltage measured across terminals of the switching device, wherein the absolute peak value corresponds to one of a plurality of half cycles present within the gap voltage measured at an instant preceding the first time instant; and on determining the first RDDS value to be less than the absolute peak value of any one of the plurality of half cycles of the gap voltage, causing to control switching of the switching device at a second time instant which is offset with respect to the first time instant such that the absolute peak value of the gap voltage is not to intersect with the range defined by the first RDDS value and the second RDDS value.

2. The method as claimed in claim 1 , wherein the method comprises: receiving a switching command from an external device for switching the switching device, wherein the switching command comprises a value of the gap voltage at which the switching of the switching device is to be caused, wherein the value of the gap voltage is determined based on a switching instant voltage lying between a zero voltage and a peak voltage; and calculating the first time instant based on the received switching command, wherein the first time instant is calculated based on an operating time of the switching device and a delay added to cause switching at the switching instant voltage on the gap voltage.

3. The method as claimed in claim 2, wherein the causing to control switching of the switching device at a second time instant comprises: on determining the first RDDS value to be less than the absolute peak value of the half cycle of the gap voltage which is adjacent to and measured at an instant preceding the first time instant, causing to control switching of the switching device at the second time instant, wherein the second time instant is delayed by the offset withrespect to the first time instant such that the first RDDS value is greater than the absolute peak value of the gap voltage.

4. The method as claimed in claim 2, wherein the causing to control switching of the switching device at a second time instant comprises: on determining the first RDDS value to be greater than or equal to the absolute peak value of the half cycles of the gap voltage measured at the instant preceding the first time instant and the switching instant voltage to be zero, determ ining a first peak value of a first half cycle of the gap voltage which is adjacent and preceding the first time instant and a second peak value of a second half cycle of the gap voltage which is adjacent and occurring after the first time instant; and identifying a plurality of instants when the RDDS values is equal to the absolute values of the half cycles of the gap voltage measured at the instant preceding the first time instant, wherein the plurality of instants comprises a prior pre-strike instant and a later pre-strike instant; and causing to control switching of the switching device at the second time instant which is delayed by the offset with respect to the first time instant such that a RDDS characteristic line corresponding to the first RDDS value is to no longer intersect with the preceding half cycles of the gap voltage.

5. The method as claimed in claim 4, wherein the first peak value is greater than the second peak value.

6. The method as claimed in claim 4, wherein the first peak value is less than or equal to the second peak value.

7. The method as claimed in claim 2, wherein on determining the second RDDS value to be greater than the absolute peak value of the half cycle of the gap voltage measured at the instant preceding the first time instant and the switching instant voltage to be peak voltage, the method comprises: identifying the plurality of instants when at least the first RDDS value is less than the absolute values of the half cycle measured at the time instants preceding thefirst time instant and occurring after the first time instant, wherein the time instants comprises a prior pre-strike instant and a later pre-strike instant; and causing to control switching of the switching device at the second time instant which is pre-empted by the offset with respect to the first time instant such that the prior pre-strike instant and the later pre-strike instant becomes equidistant from the peak of the gap voltage.

8. The method as claimed in claim 1 , wherein the method comprises: comparing the plurality of RDDS values with a threshold value; and on determining any one of the RDDS values to exceed the threshold value, shifting the first time instant from the present half cycle of the gap voltage to a half cycle present adjacent and occurring after the first time instant.

9. The method as claimed in claim 1 , wherein the first RDDS value and the second RDDS value are based on mechanical aging of the switching device, dielectric aging of the switching device, and combination thereof.

10. The method as claimed in claim 1 , wherein each of the plurality of half cycles is associated with a different frequency.

11. An intelligent electronic device (IED) for performing controlled switching of a switching device, the IED comprises: a memory; a processor coupled to the memory, wherein the processor is to: determine a first rate of decrease of dielectric strength (RDDS) value and a second RDDS value of the switching device at a first time instant, wherein the first RDDS value and the second RDDS value define a range between which a RDDS value of the switching device is to vary; compare at least the first RDDS value with an absolute peak value of a gap voltage measured across terminals of the switching device, wherein the absolute peak value corresponds to one of a plurality of half cycles present within the gap voltage measured at an instant preceding the first time instant; andon determining the first RDDS value to be less than the absolute peak value of any one of the plurality of half cycles of the gap voltage, cause to control switching of the switching device at a second time instant which is offset with respect to the first time instant such that the absolute peak value of the gap voltage is not to intersect with the range defined by the first RDDS value and the second RDDS value.

12. The IED as claimed in claim 11 , wherein the processor is to further: receive a switching command from an external device for switching the switching device, wherein the switching command comprises a value of the gap voltage at which the switching of the switching device is to be caused, wherein the value of the gap voltage is determined based on a switching instant voltage lying between a zero voltage and a peak voltage; and calculate the first time instant based on the received switching command, wherein the first time instant is calculated based on an operating time of the switching device and a delay added to cause switching at the switching instant voltage on the gap voltage.

13. The IED as claimed in claim 12, wherein to cause to control switching of the switching device at a second time instant, the processor on determining the first RDDS value to be less than the absolute peak value of the half cycle of the gap voltage which is adjacent to and measured at the instant preceding the first time instant; is to: control switching of the switching device at the second time instant, wherein the second time instant is delayed by the offset with respect to the first time instant such that the first RDDS value is greater than the absolute peak value of the gap voltage.

14. The IED as claimed in claim 12, wherein to cause to control switching of the switching device at a second time instant, the processor, on determining the first RDDS value to be greater than or equal to the absolute peak value of the half cycles of the gap voltage measured at the instant preceding the first time instant and the switching instant voltage to be zero, is to: determine a first peak value of a first half cycle of the gap voltage which is adjacent and preceding the first time instant and a second peak value of a second half cycle of the gap voltage which is adjacent and occurring after the first time instant; andidentify a plurality of instants when the RDDS values is equal to the absolute values of the half cycles of the gap voltage measured at the instant preceding the first time instant, wherein the plurality of instants comprises a prior pre-strike instant and a later pre-strike instant; and control switching of the switching device at the second time instant which is delayed by the offset with respect to the first time instant such that a RDDS characteristic line corresponding to the first RDDS value is to no longer intersect with the preceding half cycles of the gap voltage.

15. The IED as claimed in claim 14, wherein the first peak value is greater than the second peak value.

16. The IED as claimed in claim 14, wherein the first peak value is less than the second peak value.

17. The IED as claimed in claim 12, wherein on determining the second RDDS value to be greater than the absolute peak value of the half cycle of the gap voltage measured at the instant preceding the first time instant and the switching instant voltage to be peak voltage, the processor is to: identify the plurality of instants when at least the first RDDS value is less than the absolute values of the half cycle measured at the time instant preceding the first time instant and occurring after the first time instant, wherein the plurality of instants comprises a prior pre-strike instant and a later pre-strike instant; and cause to control switching of the switching device at the second time instant which is pre-empted by the offset with respect to the first time instant such that the prior pre-strike instant and the later pre-strike instant becomes equidistant from the peak of the gap voltage.

18. The IED as claimed in claim 11 , wherein the processor is to further: comparing the plurality of RDDS values with a threshold value; and on determining any one of the RDDS values to exceed the threshold value, shifting the first time instant from the present half cycle of the gap voltage to a half cycle present adjacent and occurring after the first time instant.

19. The IED as claimed in claim 11 , wherein the first RDDS value and the second RDDS value are based on mechanical aging, dielectric aging, and combination thereof.

20. The IED as claimed in claim 11 , wherein a frequency of a given half cycle from amongst the plurality of half cycles is different from a frequency of a preceding half cycle and a frequency of half cycle occurring after the given half cycle.

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